Beating a dead horse wheel size thread..lol

[Alex41]

Ok...I'm no stranger to G bodies, however, this will be my first attempt at a frame notch and large wheel fitment. I've gone over nearly every thread on how to notch and roll fenders but haven't really seen the answer I'm looking for specifically.

So......I want to go with a 15x10 wheel with a 295 50 15 tire on my 78 Malibu. I've already rolled the fenders and will be doing a notch in the frame. I plan on lowering the car where the fender juuuust tucks the rear tire. The million dollar question here is, how much frame notch do I have to do to achieve this? To the seam, past the seam, further?? I will also be moving the tubs in as well. The follow up question is, what backspacing would be best on said set up? Thanks in advance, and if anyone has pictures, please feel free to share.

 

[superbon54]

I notched wall to wall using 1/4” plate, trimmed the lips to about 3/8” and am running a 315/35-17 on a 11” wide wheel with 6 3/4” backspacing. I have about 1/2” minimum clearance to the frame and the lip.

 

[scoti]

Ok...I'm no stranger to G bodies, however, this will be my first attempt at a frame notch and large wheel fitment. I've gone over nearly every thread on how to notch and roll fenders but haven't really seen the answer I'm looking for specifically.

So......I want to go with a 15x10 wheel with a 295 50 15 tire on my 78 Malibu. I've already rolled the fenders and will be doing a notch in the frame. I plan on lowering the car where the fender juuuust tucks the rear tire. The million dollar question here is, how much frame notch do I have to do to achieve this? To the seam, past the seam, further?? I will also be moving the tubs in as well. The follow up question is, what backspacing would be best on said set up? Thanks in advance, and if anyone has pictures, please feel free to share.

Multiple things that impact this:

Rear end width.
Ride height.
Chassis/suspension mods.
And the wild-card: personal preferences.

I just did a test fit of an 18x8" wheel w/5"BS under the rear of a '78 Malibu (this was wheel only). I was able to slide a piece of 1"x1" square tubing behind the wheel (between wheel lip & unmodified frame/tub + stock width housing) w/a minimal amount of clearance remaining (1/8 - 3/16" maybe). So once you factor in the tire, you'll most likely need to trim to the seam unless you trim the outer wheel well lip/roll it significantly. The issue might be your wheel diameter. A deeper back-spaced wheel might be easier to do but the suspension items have to clear. Brake stuff & shocks need to be considered more when thinking mods through & using a 15" diameter wheel. Less back space puts you closer to the outer edge which is where how the vehicle sits (ride height) comes into play.

My buddy cut the frame to the seam & we put a 10" wheel w/6"BS under the rear of a 79 Bu (20x10; 295mm tire). He cut the tubs to install taller tubs as he wanted the clearance to run a tall tire/very low ride height (he has a thing for that). Not sure if its 100% necessary to mini-tub if only going to the seam. I know he regretted cutting the tubs w/o checking the fit of things first once he did it.

I did the test fit mentioned above for a planned 18x9" wheel w/5.25"BS & 255 or 275mm tire (it will depend on what I run in the front). My intent is as much width as I can w/o cutting the frame/tub. This car is tucking tire though (3-4" lowered rear).

 

[scoti]

I notched wall to wall using 1/4” plate, trimmed the lips to about 3/8” and am running a 315/35-17 on a 11” wide wheel with 6 3/4” backspacing. I have about 1/2” minimum clearance to the frame and the lip.

View attachment 163681

You need to put the disclaimer in there that you're also running a wider than stock rear housing. I recall you mentioning it's 1-1.5" wider than a stock housing?

 

[superbon54]

You need to put the disclaimer in there that you're also running a wider than stock rear housing. I recall you mentioning it's 1-1.5" wider than a stock housing?

You’re correct...... kinda. The wheels are actually 7 1/4” BS on a 1” wider rear. I stated the BS measurement I did to avoid the potential confusion in the math. Most people will measure their car with factory geometry, not my Frankenstein setup.

 

[Alex41]

The rear end is a GM 8.5
Hard to say on ride height but I'd like to just tuck the top of a 26.6" tire
I will be going with coilovers in the rear but that shouldn't affect anything since it will be inboard of the frame
And preference is that wide 295 under the back.

 

[64nailhead]

You need to measure. All of the G’s aren’t the same. We have an 80 Cutlass that a 275/60R15 barely clears the fender with 1/8” clearance on the frame, and an 84 MC that there is almost an 1”of clearance from fender to frame. Maybe it’s only 3/4”, but it’s noticeably larger than the 80.

My point being is to measure. The easiest way to do this is to remove the rear springs and support the frame on stands and then jack up the rear with the torque arms hooked up. Then measure twice (at least) and start hacking.

 

[superbon54]

My point being is to measure. The easiest way to do this is to remove the rear springs and support the frame on stands and then jack up the rear with the torque arms hooked up. Then measure twice (at least) and start hacking.

This! I bet I have a couple hours of measuring and calculating to ensure the frame, rear end, wheels, tires, tubs and body all did what I wanted when assembled.

 

[scoti]

The rear end is a GM 8.5
Hard to say on ride height but I'd like to just tuck the top of a 26.6" tire
I will be going with coilovers in the rear but that shouldn't affect anything since it will be inboard of the frame
And preference is that wide 295 under the back.

So, stock width housing, coil-overs w/non-stock inboard mounting location, approximately a ~26" fender lip height (tire tucked 5/8"), & 15" wheel diameter for your particulars.

First thing you need to do is measure what you have. Reverse engineer/calculate from there. Pop a wheel/tire that fits in place. Take the springs out & adjust the height @ the fender lip close to the approximate height of your particulars. Get some measurements of the clearance & the wheel/tire used for the process. Let us know what you get.

 

[Streetbu]

I run 275/35/18 on 18x9.5" with 5.25" backspacing all the way around. Running a GN 8.5" rear end, so the same exact width a stock 7.5", I notched the frame to the seam, and have about a 1/2" of clearance... the tire is about 1/2" away from the fender lip at ride height. Ride height is 26.25" to the rear wheel lip, so pretty low. There is NO way I could've fit any 275 tire in my car with out rubbing. There just wasn't room. Don't know why, but I highly recommend you measure, then remeasure...